FILE - In this Saturday, June 18, 2016 file photo, Russian Defense Minister Sergei Shoigu, second left, visits the Hemeimeem air base in Syria. Shoigu said on Thursday, July 28, 2016 that Russia and the Syrian government will open humanitarian corridors and offer a way-out for Islamic State fighters wanting to lay down their arms. (Vadim Savitsky/Russian Defense Ministry Press Service Pool Photo via AP, file)

"If it is a genuine humanitarian proposal, then clearly it would be accompanied by an end to the bombing campaign and by Russian support for other aspects of this comprehensive approach to the humanitarian situation in Aleppo," he told reporters in New York.

Using the corridors to allow aid into Aleppo "would be welcome," Rycroft said.

"But clearly, the U.N. and the rest of us cannot be complicit in anything else — for instance, any form of emptying of Aleppo, or preparing for an onslaught in Aleppo, or indeed any continuation of this medieval siege of Aleppo which is going on," he said.

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8:35 p.m.

The U.S. ambassador to the United Nations has posted what she calls a "chilling letter" from Syria's U.N. envoy saying the army has informed civilians in embattled eastern Aleppo that it has secured safe passage out for those who want to leave.

The letter from Ambassador Bashar Ja'afari to the U.N. Security Council said the Syrian government has also "allocated temporary accommodation" for those who leave and is keen "to provide them with their livelihood needs."

The U.N. humanitarian chief says the Russian proposal for humanitarian corridors in Aleppo must be guaranteed by all parties and "no one can be forced to flee, by any specific route or to any particular location."

Undersecretary-General Stephen O'Brien said Thursday that his proposal for weekly 48-hour humanitarian pauses to enable aid deliveries across borders and conflict lines "is what we as humanitarians require."

"This is to ensure that we are able to see for ourselves the dire situation of the people, assess their needs, adjust to logistical constraints and assist people where they are now with their life-saving and protection needs," he said in a statement issued at U.N. headquarters.

O'Brien reiterated the U.N. demand for "safe, regular and sustained access" to 250,000 people trapped behind front lines and stressed that "all options must be considered."

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5:30 p.m.

Rights watchdog groups are warning the Syrian government that opening safe passages to civilians trapped in eastern Aleppo city does not give Syrian and Russian forces carte blanche to further blockade the opposition-controlled territory or target it with indiscriminate fire.

Nadim Houry, the deputy Middle East director at Human Rights Watch, tells The Associated Press Thursday that the safe passage offer, "doesn't mean that the people who stay behind are legitimate military targets."

Syrian government forces backed by Russian air power have gradually tightened a siege over eastern Aleppo in recent weeks, and on Thursday said they would offer civilians and militants who lay down their arms safe passage out of the district. But Amnesty International demanded "unfettered and impartial humanitarian assistance" to the district.

Amnesty said in a press release that, "Providing safe routes for those civilians who wish to flee Aleppo city will not avert a humanitarian catastrophe. It is not a substitute for allowing impartial humanitarian relief for civilians who remain in opposition-held areas of the city or other besieged areas, many of whom will be skeptical about government promises."

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4 p.m.

Al-Qaida's deputy leader is urging the network's Syria branch to do what it takes to preserve jihad in the war-torn country, an apparent endorsement of the Nusra Front's plans to split from the parent organization.

Senior Nusra Front figures have been discussing plans to dissociate from al-Qaida. The discussions come amid calls from Russia to target the group, which collaborates with other rebel groups, including those backed by the U.S.

In a six-minute recording Thursday, Ahmed Hassan Abu el-Kheir — currently Ayman al-Zawahri's deputy— says al-Qaida instructs "the leadership of the Nusra Front to go ahead with what protects the interests of Islam and Muslims and what protects jihad" in Syria.

He also urged the Nusra Front to unite with other factions against "Crusaders" and form a good "Islamic government."

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3:05 p.m.

The U.N. envoy for Syria says he wants to see how the United Nations could coordinate with Russia on its plan to help civilians and opposition fighters who lay down their weapons outside the northern Syrian city of Aleppo.

Staffan de Mistura says the city is "de facto" besieged after Russian-backed Syrian government forces and their allied troops closed in on Aleppo's main rebel enclave.

De Mistura told reporters on Thursday that he understood Russian military experts "and perhaps (some) from the U.S." were headed to Geneva, "most likely in order to discuss the devils in the details" of the two powers' efforts to end the fighting in Syria.

De Mistura says he will travel to the Iranian capital of Tehran "to make sure the Iran authorities are well on board" with a U.S.-Russian plan laid out last week in Moscow.

Iran is a staunch supporter of Syrian President Bashar Assad.

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1:40 p.m.

The governor of Syria's Aleppo province says on state TV that three crossings have opened for residents of the besieged parts of the city of Aleppo.

Mohammed Marwan Olbi says the government will offer those who leave temporary accommodation.

The TV says fliers have already been dropped on Thursday on rebel-held besieged parts of Aleppo city, urging people to take the government's offer of humanitarian corridors.

There are no signs yet that residents have converged on the crossings. The TV also aired a call from Aleppo clerics, urging armed groups to drop their weapons.

Syria's President Bashar Assad has offered an amnesty to rebels who lay down their arms and surrender to authorities over the next three months. The government completely closed the main road into the rebel-held areas on July 17, effectively besieging them and 300,000 residents.

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12:15 p.m.

Syrian state media are reporting that government forces have taken another neighborhood from rebels in the contested northern city of Aleppo.

Thursday's report came as the Russian government says safe passage is being offered out of rebel-held areas of the city to civilians and rebels who lay down their arms.

The state SANA news agency says the military has taken control of the Bani Zeid neighborhood and has begun clearing land mines there. It says dozens of gunmen have laid down their weapons and surrendered in the neighborhood.

The Britain-based Syrian Observatory for Human Rights monitoring group says government forces have taken command of large swaths of Aleppo's Bani Zeid. Pro-government forces have been steadily tightening a siege on rebels in the eastern part of the city since last week.

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11:55 a.m.

Russian Defense Minister Sergei Shoigu says Moscow is sending a top general and experts to Geneva at request of U.S. Secretary of State John Kerry to discuss the crisis surrounding the embattled Syrian city of Aleppo.

The announcement comes after Russia said its forces and the Syrian government would open humanitarian corridors outside Aleppo and offer a way-out for fighters wanting to surrender.

Shoigu said in televised remarks on Thursday that President Vladimir Putin, in response to a request by Kerry, ordered a general and experts to Geneva.

Syria's President Bashar Assad has offered an amnesty to rebels who lay down their arms and surrender to authorities over the next three months.

The amnesty offer was issued through a decree on Thursday and urged that all detainees be freed. It says that those who might set free their captives will be exempted from punishment if they turn themselves in within a month. It was reported by state-run news agency SANA.

The offer coincides with a government offensive that has succeeded in completely encircling rebels in the eastern part of the city of Aleppo.

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11:00 a.m.

Russian Defense Minister Sergei Shoigu says Russia and the Syrian government will open humanitarian corridors and offer a way-out for opposition fighters wanting to lay down their arms.

Syrian government forces and allied troops have tightened the noose on the main rebel enclave in the city of Aleppo, urging fighters there to surrender. Humanitarian groups have warned of a major catastrophe if the siege on the rebel-held parts of Aleppo continued.

Shoigu said in televised comments Thursday that President Vladimir Putin has a "large-scale humanitarian operation" that will be launched outside Aleppo to "help civilians who were taken hostage by terrorists as well as fighters who wanted to lay down the arms." Shoigu mentioned three humanitarian corridors as well as food and first aid points outside the city.

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This item has been corrected to show that Shoigu was referring to Syrian opposition fighters, not IS fighters.